The 3 most important things every startup founder should focus on

Every early-stage startup founder should have only two focuses until they find a Product-Market Fit.
The focus lowers to only one thing after that point.

Early-stage focus : Product & Market

As an early-stage startup, you should have only one focus which is finding a Product-Market Fit (PMF).

You have at this time only two focuses : building an awesome product & finding customers who will buy this product (or if you are an adept of Lean Startup : Finding potential customers and then building a great product for them)

Unless you are able to build a product and sell it by yourself (which is what I did in the early stages of Datananas, but requires to be a bit schizophrenic) you will need a co-founder. This is why early-stage statup team are generally composed by 2/3 peoples :

The Tech guy who builds something

The Hustler who sells it

In my opinion, this is why the best early-stage startup founders are fast-learners : they can do software development, UX, marketing, sales, etc… all at the same time. They talk to a customer and build the ideal product for them at the same time and avoid information loss. They are not the best in the world for each job (of course not) : but whatever they have to do, they will find a way.

Post-PMF focus : HR

This might sound stupid that hiring and keeping the best talents is such an important thing in a company, and it is not the primarly thing taught in Business Schools. Human Resources should be the only focus after the PMF.

You built something cool, and people buy it. Great.
The question is now : How will you scale the business ?
Tha answer : by selling more, and building some other great features/products.

You won’t scale your early-stage startup by yourself, and you need to find people that are better than yourself for each task. If the early-stage founder can do everything, the post-PMF founder is able to find people that are better than him for each job.

How to hire superstars

I know two books that are worth reading about hiring great people :

Smart and Gets Things Done by Joel Spolsky (Microsoft, Stack Overflow, Trello), which focuses on hiring great Software Developers. The title sums up what you should be looking for in Engineering talents : they are smart and they get things done

The focus remains the same as in early-stage (Product and Market), but with a slight difference : finding great people to build the next products and finding great people to execute the sales strategy.